A process and apparatus for the continuous cleaning of contaminated waste air, for example waste air containing organic vapors, is described in U.S. Pat. No. 4,930,294 (Meier). In the process and apparatus of this '294 patent, an adsorption media is stored in a tank or vessel to define an adsorption bed, and vapor-containing waste air is supplied to the bed. In passage of the waste air through the bed, the organic vapors collect on or are adsorbed by the bed media, whereupon the air from which the contaminants or vapors have been removed then passes out of the bed for discharge as desired. Thereafter the bed on which the contaminants are collected or adsorbed is isolated from the waste air supply, and microwave energy is supplied to heat the bed media and effect release of the vapors from the bed media, with the vapors when being sucked out of the bed for collection. The process and apparatus of the type described in the '294 patent, as well as variations of such process and apparatus, are known, but nevertheless have not proven to operate in a desirable and efficient manner.
In known arrangements having the overall structure and function as briefly summarized above, such arrangements have typically supplied the microwave energy to the bed at one of the bed peripheral surfaces, such as at an upper end of the bed as in the '294 patent, and the overall arrangement is such as to provide undesired concentration of microwave energy at selected regions of the bed. For example, when the microwave energy is supplied to the upper end of the bed as in the '294 patent, excessive heating can occur at the upper end of the bed, and insufficient heating can occur at the lower end of the bed, whereby a significant temperature gradient exists both longitudinally and/or transversely within the bed so that efficient and economical release and recovery of the contaminants or vapors is not achieved. This can also cause localized heating of such a nature as to damage the bed media. The contaminants also have a long travel path from the upper to the lower end of the bed, which reduces the efficiency of removal.
Accordingly, this invention relates to an improved process and apparatus for removing contaminants such as volatile organic compounds (VOCs) from waste air or gas by an adsorption media, and in particular to an improved process and apparatus which provides more effective separation of the volatiles from the adsorption media and the regeneration thereof so as to overcome disadvantages associated with prior processes and apparatus of this general type.
More specifically, in one embodiment of the improved process and apparatus of this invention, the contaminated air or gas stream is fed into an adsorption chamber containing a bed of adsorption media therein. This chamber in the preferred embodiment is defined by a generally cylindrical vessel, and the adsorption media preferably comprises a polymeric material in particulate or bead form. The volatiles such as VOCs are adsorbed by the adsorbent bed as the gas stream passes therethrough, with the air or gas stream then being discharged. The adsorbent bed is defined in surrounding relationship to an elongate hollow guide tube which extends longitudinally along the central axis of the bed. A microwave generator or transmitter is connected to and supplies microwave energy into the guide tube which functions as a tubular waveguide. This waveguide has a plurality of slots or openings formed therein which function as radiators for the microwave energy. The microwave energy passes radially outwardly from the waveguide into the surrounding bed throughout the entire length of the waveguide and bed to effect reasonably uniform heating both longitudinally and radially. This heating effects release of the volatiles from the adsorbent bed media, which volatiles are then sucked out of the bed and suitably collected.
In the process and apparatus of this invention, as aforesaid, the waveguide is provided with radiator openings formed therein in such a pattern as to provide for substantially uniform discharge of microwave energy therefrom throughout the length of the waveguide. For this purpose the waveguide may, in one variation of the invention, be provided with uniform openings throughout the length of the waveguide, with the density of these openings being increased throughout the length of the waveguide as the waveguide projects away from the microwave generator. More specifically, the size, shape, density and positional arrangement of the radiator openings are determined based upon the geometry of the vessel and particularly the geometry of the media bed and waveguide, as well as the frequency of the microwave energy supplied to the waveguide. A further variation, to achieve the desired uniformity of energy discharged throughout the waveguide length, is to increase the size of the openings along the waveguide length as the openings are spaced further from the microwave generator.
In another embodiment of the improved process and apparatus of this invention, the contaminated air or gas stream is utilized as a fluidizing substance which is part of a fluidized adsorption bed, which fluidized bed contains therein an adsorption media which is fluidized or maintained in suspension by the gas stream. In this manner the adsorption media adsorbs undesired volatiles from the gas stream so that latter is cleansed. The media can then be supplied to a regenerative vessel which has the general properties described above, namely an annular media chamber which surrounds a waveguide tube so that microwave energy can be discharged in a reasonably uniform manner both circumferentially and axially along the waveguide for distribution radially outwardly into the annular media bed to effect release of the volatiles from the media. Following release and removal of the volatiles, the media can then be discharged from the regenerative vessel and resupplied to the fluidized bed.
Other objects and purposes of the present invention will be apparent to persons familiar with processes and arrangements similar to the present invention upon reading the following specification and inspecting the accompanying drawings.